More external sources for submissions

[JanKoppe]

As proposed by @nuest:

• External source
  • something generic, e.g. /upload/remote with POST and then we figure out from the provided JSON payload what it is (e.g. git URL)

[nuest]

Maybe we can collect some more examples of what "external sources" could be (not saying we're going to implement any of these, not sorted):

• link to a public shared folders of a cloud hosting solution
  • Dropbox
  • Sciebo/ownCloud
  • OSF
  • invitation to a privately shared folder (ownCloud)
• link to a GitHub project
  • use a branch by name
  • use a release by name
• link to a git repo (URL for clone command)
• link to a BitBucket project
• link to a gitlab project
• link to a remotely available archive/zip file (e.g. from figshare or Zenodo, or a GitHub release)
• DOI (e.g. linking to a Zenodo project)

[nuest]

@LukasLohoff fyi - some stuff we have discussed a long time ago that is related to your "loader" component.